This invention relates in general to battery monitoring devices and, in particular, to a sensor system for monitoring the level of liquid electrolyte in a wet cell battery and also for sensing the stratification of electrolyte indicating a change in the specific gravity at various electrolyte levels.
At high charge rates, a portion of the water in the electrolyte of a lead-acid storage cell is lost by electrolysis. If, as a result of this loss and losses by other mechanisms such as evaporation, the electrolyte level drops so low as to expose the surface of the cell electrodes, the cell may be quickly and permanently damaged. On the other hand, if a cell is overwatered prior to the charging of the battery, the electrolyte may overflow during or following charging with deleterious consequences.
Accurate and reliable information about electrolyte level is particularly valuable in cases where a high capacity, many cell battery system is used to provide operating or emergency power. Typically, the electrolyte level in such systems is monitored by periodic visual inspection of randomly selected cells (if the battery container is transparent) or by opening the cells and inserting a dip tube to determine the liquid level. Obviously, this approach is of limited effectiveness in detecting problems and is also time consuming. Often batteries are located in inaccessible areas further complicating manual monitoring.
Many methods have been proposed to monitor the level of electrolyte in a wet cell battery. Generally, these prior methods generate a signal when the liquid in a cell falls below, or rises to, a predetermined level. However, these prior methods have frequently proven to be unreliable, inaccurate or unduly complicated. Further, large lead-acid batteries suffer from the problem of electrolyte sulfation and stratification. When a cell is charged, acid is formed at the plates and this more dense acid tends to sink to the bottom of the cell. In tall cells, where diffusion is insufficient to overcome the density gradient, it is necessary to know when stratification occurs in order that some mechanical agitation or other means can be provided to circulate the electrolyte and maintain a homogeneous electrolyte.
A simple, reliable, and accurate sensor system for indicating the instantaneous liquid level and also for indicating when stratification occurs, which is capable of transmitting the data to a remote location, is highly desirable. The present invention is intended to provide such a sensor system. A device for merely monitoring the specific gravity of battery wet cells also is possible with the techniques of this invention.